The terminology “analyzer” in the sense of this invention means a measuring apparatus of process automation technology, which measures with a wet chemical method certain concentrations of substances, for example, an ion concentration in a medium to be analyzed. For this, a sample is removed from the medium to be analyzed. Most often, the sample is removed fully automatically by the analyzer, for instance, by pumps, hoses, valves, etc. For determining the concentration of a substance of a certain species, reagents specially developed for the respective concentration of substance and stored availably in the analyzer housing are mixed with the sample to be measured. A color reaction of this mixture caused thereby is then measured by means of a suitable measuring device, for example, by means of a photometer. More exactly stated, sample and reagents are mixed in a cuvette and measured with different wavelengths using the sent light method. Based on the light absorption and a furnished calibration model, the measured value is, in this way, ascertained on the receiving side.
In designing a corresponding calibration model, the following difficulties result: The relationship between absorption and concentration of the substance is not linear and is influenced by external disturbance variables. FIG. 1 shows a typical graph of absorbed light as a function of the concentration of a substance, here, by way of example, ammonium, for seven different wavelengths 1-7. It is to be seen that the curves are not linear, above all, at the higher concentrations of the substance. Users additionally desire that the analyzer be able to operate as long as possible self-sufficiently, i.e. without (re-) calibrating and (re-) adjusting or replacement of reagents.